Various types of electromagnetic fuel injectors are used in the fuel injection systems of internal combustion engines. Such injectors, as well as other solenoid controlled valve structures, incorporate a solenoid armature that is located between a center pole piece of the solenoid and a fixed valve seat whereby the armature is operable as a valve member. Examples of such electromagnetic fuel injectors or solenoid controlled valve structures are described in U.S. Pat. Nos. 4,515,129 issued May 7, 1985 to Stettner and 4,572,436 issued Feb. 25, 1986 to Stettner et al. The above identified references disclose arrangements in which an armature/valve is biased towards a normally closed position against a fixed valve seat by a spring member. Energization of the solenoid draws the armature/valve, against the bias of the closing spring, into abutment with the lower end of the solenoid center pole through attraction of the solenoid magnetic field. Following termination of the electrical signal, the solenoid magnetic field collapses and the armature/valve returns to its closed, seated position relative to the valve seat, under the bias of the return spring.
It is desirable to precisely control the flow of fuel through the valve seat, and thus the injector, in order to meet engine performance requirements. It is also desirable that, for a given application, all injectors in a particular engine meter equivalent quantities of fuel to the engine cylinders upon application of a predetermined electrical input. As such, the injector flow curve must be adjusted to meet a nominal set of injector flow requirements. In general, a solenoid operated injector is a linear device that will meter fuel on a per-pulse basis which is proportional to the input. The specific relationship between pulse-width and fuel delivered is dependent upon the static flow of the injector, which is typically controlled through armature stroke, and dynamic response or flow, which is typically a function of spring load and magnetic field characteristics.